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Hi guys, I have a bit of a weird problem I could really use your help with. My QIDI 3D Dual Extruder is having issues printing in the center of the bed. A little background - a few months ago I removed the factory blue sheet that was on the heated bed. I replaced it with a 1/8" pane of glass from a local framing shop. The glass is not the exact size (slightly too small), and I am using four corner clips to hold it in place. It's pretty stable. Sometimes I use a binder clip on one side. The heating is fine. I am printing exclusively in PLA on the right extruder. The left extruder has no filament and the nozzles were recently leveled.

Anyway, the issue is any part of the model that is roughly around -50mm to 50mm on the X axis gets no filament laid down. In other words, if I were to draw a straight line, you would see a light gap in the center. I've gotten around this temporarily but positioning my models towards the corners of the bed but this is not the best solution since some models are very large or very long and need to cross the origin. I know this sounds like a leveling issue and I've leveled, I swear, over a dozen times already. I am not sure what else there is to do. I suppose it's possible my glass isn't flat but ... that would kind of go against the definition of glass - it's supposed to be perfectly flat. I ordered another sheet - 3mm borosilicate and that's arriving this week. Maybe I'll have better luck.

Also when leveling. Only level with the nozzle to be used directly over each leveling screw. The center of the bed can seem to be a bit higher due to inherent "sag" from the gantry. This is normal on most of these style printers.
1/8" glass is thin enough to bend so if the bed is really bad and the glass is clamped down at the corners it is possible to distort it.

And frequently, when the filament does not flow within a specific area of the print surface, it is because that area is too close to the nozzle. This is precisely what would happen if the extruder Y-Axis naturally sags down toward the print surface slightly, and the nozzle is too close. Maybe try adding a little more space when you "level" the bed.

One other item, you mentioned only printing from the Right extruder. Commonly when printing PLA, the best results are obtained with the use of a cooling blower/fan. Unless you have customized the stock QiDi blower's output duct work, the QiDi's fan really only blows air very well onto the print bed around the left extruder. Switching which extruder you use and turning on the fan after layer 1 is completed may significantly improve your prints. If you have issues with the PLA sticking, some glue stick can always help out.

Whoa guys, sorry for not coming back to this sooner. I got so much useful ideas I hadn't thought of. For example, I usually level over the areas I know my test will print. I never thought about leveling only over the screws. And you're right DaveB, I haven't modified my setup and it makes sense that the PLA printing from the right isn't getting the benefit of the left fan cooling. I also noticed that when no filament comes out, loosening up the space between the head and bed can help. I got a new plate of glass in but before I install it, let me implement the other suggestions you guys had! I'll report back with results. Thank you very much.

Sounds great! Your doing so good we'll load you up with more!
First rule! When you level and think it is good, do it again. Get a system that becomes second nature! Once leveled really watch what the first layer is doing and how it is extruding. What is it telling you? When you do make a change, resist changing multiple things at once. Small adjustments and try again.
The best feeling - and you'll know it - is when you see a problem and you think you know just what is needed and it actually works just as you hoped and then it all clicks and a print comes together.

Troubleshooting - eliminate the most obvious, simplest things first because that is usually what it is. Like when filament does extrude or extrudes poorly on the first layer. Loosen the gap and see what happens, just as you have found. Everyone will have good advice on a problem but so many over complicate an issue. Just keep it simple and remember - these are machines and even though you will come to believe it has a mind of its own at times, it still only does what it is told to do!

Glass is easy and you will wonder how you lived without it. Just remember to print a shim for the Z end stop. You need to add a spacer so the bed doesn't lift as high when the glass is in place. Search thing for a spacer and I am sure Dave will recommend one.

I ultimately went to PEI on the glass. No more sprays or glue. Works good.

I personally like to tighten the bed plate springs instead of using a shim. Helps with holding the bed in place on those fast infills.

I have not found any benefit to having the bed be loosey-goosey because the leveling screws / springs are not tightened down. I completely agree that having the bed NOT wobble about makes for a superior print with less reflection artifacts.

Shims are intended to be used to compensate for the major shifts in the build platform Z-Axis home position that occur when different arrangements of build surface material stack-ups are placed upon or removed from the print bed.

In the ideal scenario, the springs are well compressed, the platform is level, and no shim is needed when using the thinnest of your build surface stack up options. When you choose to put in a different and thicker build surface, a shim of the perfect thickness is put in and (ideally) no adjustment of the leveling screws is then necessary.